In the past we have described a set of cell lines well characterized for their response to the different environmental conditions that signal growth inhibition, and a set antisera specific for three major cell proteins: actin, myosin and tubulin. Recently we have found evidence to suggest that both the signals and the major proteins interact intimately with the cell surface. These observations will be used to initiate a study of the links between regulation of cell shape and regulation of cell growth using normal differentiating cells as well as established cell lines. In this way, the different stable patterns of growth control induced by infection with tumor viruses, especially the tumor virus SV40 and its mutants of complementation group A, will be analyzed.